Although the sludge obtained by sewage treatment is sometimes used as a compost, its most frequent use is for land reclamation. The soil containing the sludge has heavy metals and emits an offensive odor and may be decomposed, because of the presence of the sludge. Such problems may be solved by burning the sludge to ashes and using the ashes for land reclamation. However, this entails no small cost because fuel is required for the burning of the sludge.